Chemical and materials synthesis and its transformation is one of the core industries of world economy. Various techniques have been developed for the generation of such particles, some based on physical and some on chemical principles. In addition to particle size and composition, particle shape plays an important role in modulating its electronic and chemical properties. Since the collective properties of particle assemblies are also critically dependent on the shape of the superstructures. Numerous substances are synthesized using processes that require non-ambient temperatures and/or non-ambient pressures that require capital-intensive equipment. Methods that can produce useful chemicals and materials at conditions closer to ambient conditions and use simple equipment are economically, ecologically, and environmentally more desirable.
Significant research efforts have been devoted for nanostructure processing as a means of achieving materials with commercial requirements in areas as diverse as electronics, pigments, cosmetics, ceramics and medical industries, (Mann et al., Nature., 1996, 382: 313-318;).
Langmuir monolayers have been shown to induce oriented crystallization from solution of proteins (Uzgiris and Komberg et al Nature., 1983, 301, 125) and other organic and inorganic compounds (Landau et al Nature., 1985, 318, 353). Mann and co-workers have studied the oriented crystallization of CaCO3 under monolayers of stearic acid (Mann et al, Nature., 1988, 334, 692; Mann et al Nature., 1988, 332, 119) Heywood and Mann have studied the oriented nucleation of BaSO4 under compressed Langmuir monolayers of long chain alkyl phosphonate resulted in plate-like out growth as well as bow-tie morphology (Heywood and Mann et al Langmuir., 1992, 8, 1492) and under n-eicosyl sulfate/eicosanoic acid monolayer resulted in unusual and complex morphology of BaSO4 crystals (Heywood and Mann et al J. Am. Chem. Soc., 1992, 114, 4681). Self-assembled monolayers (SAMs) have also been used to grown minerals-such as calcite (Aizenberg et al, J. Am. Chem. Soc. 1999, 121, 4500). This often leads to the oriented growth of CaCO3 crystals on surfaces such as terminally functionalized SAMs supported on metal films. (Kuther et al Chem. Eur. J. 1998, 4, 1834). Travaille et al. have shown interesting hexagonal organization of highly oriented calcite crystals on Au (111) films covered by a monolayer of 16-mercaptohexadecanoic acid (Travaille et al Adv. Mater. 2002, 14, 492-495). Chen et al have shown two-dimensional nanoparticle cross-linked networks were constructed by using the Langmuir-Blodgett technique, where neighboring particles were chemically bridged by bifunctional linkers at the air/water interface (Chen et al, Langmuir 2001, 17, 2878). Crystallization of Prussian blue analogues has been observed using octadecylamine monolayer as a template at the air-water interface (Choudhury et al, Langmuir 2002, 18, 7409). Controlled silanization of Sto{umlaut over ( )}ber silica particles have been prepared by using monofunctional trimethylsilyl N,N-dimethyl carbamate at the air-water interface resulted in (Tolnai et al, Langmuir 2001, 17, 2683). The Langmuir layer behavior of a polymer/magnetite nanoparticle complex at the air/water interface resulted in Fe3O4 nanoparticles with an average diameter of 8.5±1.3 nm (Kang et al, Langmuir, 1996, 12, 4345). Also the Langmuir layer behavior of arachidic acid/Á—Fe2O3 nanoparticle with an average diameter of 8.3 nm complexes was studied at the air/water interface (Lee et al J. Phys. Chem. B 2002, 106, 9341). Gold nanoparticles have been organized at the liquid-liquid interface between the gold hydrosol and benzene as well as anthracene in chloroform, where the biphasic mixture results in complete transfer of the gold nanoparticles from the aqueous to the benzene phase and the subsequent assembly of gold nanoparticles at the liquid-liquid interface (Sastry et al, Langmuir 2002, 18, 6478). Barite crystals have been grown at liquid-liquid interface between an aqueous solution of Ba2+ ions and organic solutions of chloroform and hexane containing fatty acid/fatty amine molecules by reaction with sodium sulfate resulted in flat, plate like morphology (Sastry et al, CrystEnggCom.2001, 45, 1). SrCO3 crystals have been grown at the interface between two immiscible liquids resulted in self-assembled needle shaped strontianite crystallites branching out from the seed crystal (Sastry et al, Bull. Mat. Sci. 2003, 26, 283).
U.S. Pat. No. 5,733,458 provided a method for changing the shape of the interface between two materials by applying a magnetic field, which enables the change of the interface shape in an amount at least equal to that conventionally observed on the air-liquid interface be achieved by a magnetic field of significantly lower intensity.
In all the above methods of synthesis of inorganic materials discussed, the charged interface at which crystal synthesis is carried out is static. To the best of our knowledge, there are no reports investigating the role of an expanding charged interface on inorganic material growth. We herein put forth the invention on the synthesis of various inorganic materials at a steadily expanding charged interface between two liquids in a radial Hele-Shaw cell. We observe interesting assembly, morphology and control over the crystallography of various inorganic materials such as mineral/ceramic/oxide/metal/sulfide superstructures with respect to the different experimental conditions used.
The prior art methods for the growth of various inorganic particles teaches us to grow a wide variety of these particles together with the control over their crystal size, shape and morphology but have certain limitations.
The major drawbacks of the prior art processes are:
1. Charge interface is static
2. Higher ordered superstructure is not possible
3. Large scale synthesis is not possible
4. Uniform size control is tough,
5. Complex conditions,
6. Require more maneuvering,
7. Not robust,
8. Not cost effective,
9. Not stable,
10. Morphology control is complex
Our process considerably simplifies process for the large-scale synthesis of crystalline inorganic materials with controlled shape, size and morphology and their assembly in to higher ordered structures thereof. Changing simple parameters helps controlling the shape, size and morphology and their assembly in to higher ordered superstructures.